What are fibroids? Fibroids are muscular tumors that develop inside the wall of the uterus (womb). Fibroids are almost continually benign (not cancerous). Not all women with fibroids have signs and symptoms. Women who do have signs often find fibroids hard to stay with. A few have ache and heavy menstrual bleeding. Fibroids can develop as a single tumor, or there may be many them within the uterus. They can be as small as an apple seed or as large as...